A large portion of utility consumption meter reading, such as for water, gas, or electricity, has been accomplished automatically by portable reader devices. For example, unattended reader devices are used in most drive-by reading systems to collect “meter reading data” that quantify the consumption of utility services. The unattended reader devices are typically mounted on top of vehicles that drive through a designated geographic area and are designed to be automatically operated when collecting meter reading data. In such systems, the collected meter reading data are processed later in a centralized reading and processing system. Thus, when the unattended reader devices collect meter reading data, it is critical to maintain accurate time in the reader devices to timestamp readings when they are collected and stored.
Conventionally, the reader devices rely on a time source provided by a network or Global Positioning System (GPS) for synchronization. However, there are some areas or spots where no network or GPS connection is available (e.g., when the reader device does not have connectivity through a network to a source of precise time) since the drive-by reading systems tend to cover various conditioned geographic areas. In such cases, the unattended reader devices are not always able to properly adjust their clocks to accurate time, which may result in generating inaccurate timestamps in the collected meter reading data.